Runtime: Bun + TypeScript, Node-compatible core

Status: accepted

Decision

TypeScript everywhere. Bun is the toolchain: dev runtime, test runner (bun test),
bundler, and bun build --compile produces the single-file executables that are our
primary distribution. Core packages (core, formats, lore, presets, macros,
regexkit, assembly) must not use Bun-only APIs: they stay runnable under Node so
they can be published to npm and embedded by other tools. apps/* and agent/ai
may use Bun APIs where they matter (spawn, file IO speed, compile).

Why

• The distribution goal is a single executable without a separate runtime installation. bun build --compile is the most direct path on all three OSes.
• TypeScript because the entire extraction surface from VAUDEVILLE is TS, and because
  zod schemas double as both validation and documentation.
• Node-compat core keeps the npm/embedding door open and de-risks Bun (if Bun ever
  stalls, only apps need porting).

Consequences

• CI runs core package tests under BOTH Bun and Node.
• A lint rule bans bun:* imports inside packages/ except an allowlist
  (ai, agent).